Method for controlling multiple power supplies in an image forming apparatus

Abstract

A controller operates a first power supply and a second power supply in a current detection period in which a detection circuit detects a charging current, thereby applying a superimposed voltage generated by superimposing a voltage of a first polarity and a voltage of a second polarity to a transfer member. The controller determines a surface potential of an image bearing member based on the charging current detected in the current detection period.

What is claimed is: 
     
         1 . An image forming apparatus comprising:
 an image bearing member;   a motor configured to rotationally drive the image bearing member;   a charging member configured to charge a surface of the image bearing member which is rotationally driven by the motor;   a light source configured to irradiate the surface of the image bearing member with light to form an electrostatic latent image;   a developing member configured to develop the electrostatic latent image using a toner charged to a first polarity to form a toner image;   a transfer member configured to transfer the toner image from the image bearing member to a transfer material;   a first power supply configured to generate a voltage of the first polarity, supply the voltage of the first polarity to the charging member as a charging bias, and supply the voltage of the first polarity to the transfer member;   a second power supply configured to generate a voltage of a second polarity opposite the first polarity and supply the voltage of the second polarity to the transfer member;   a detection circuit configured to detect a charging current flowing between the charging member and image bearing member; and   a controller configured to control the first power supply and the second power supply to determine a surface potential of the image bearing member based on the charging current,   wherein the controller is further configured to operate the first power supply and the second power supply in a current detection period in which the detection circuit detects the charging current, thereby applying a superimposed voltage generated by superimposing the voltage of the first polarity and the voltage of the second polarity to the transfer member, and to determine the surface potential of the image bearing member based on the charging current detected in the current detection period.   
     
     
         2 . The image forming apparatus according to  claim 1 , wherein
 the voltage of the first polarity and the voltage of the second polarity used in the current detection period are adjusted so that an electric discharge occurs between the charging member and the image bearing member, and an electric discharge does not occur between the transfer member and image bearing member.   
     
     
         3 . The image forming apparatus according to  claim 1 , wherein
 the current detection period includes a first period and a second period,   an absolute value of the voltage of the first polarity in the first period is smaller than an absolute value of the voltage of the first polarity in the second period,   in the first period, the voltage of the second polarity is not supplied to the transfer member,   in the second period, the voltage of the second polarity is supplied to the transfer member, and   the controller is further configured to determine the surface potential of the image bearing member based on a first charging current detected by the detection circuit in the first period and a second charging current detected by the detection circuit in the second period.   
     
     
         4 . The image forming apparatus according to  claim 3 , wherein
 the controller is further configured to determine a dark portion potential that is a surface potential of the image bearing member by dividing a difference between the first charging current and the second charging current by a difference between the voltage of the first polarity supplied to the transfer member in the second period and the voltage of the first polarity supplied to the transfer member in the first period to obtain a current change amount per unit voltage, and dividing the second charging current by the current change amount.   
     
     
         5 . The image forming apparatus according to  claim 1 , wherein
 the current detection period includes a first period, a second period, and a third period,   an absolute value of the voltage of the first polarity in the first period is smaller than an absolute value of the voltage of the first polarity in the second period, the absolute value of the voltage of the first polarity in the first period is smaller than an absolute value of the voltage of the first polarity in the third period,   in the first period, the voltage of the second polarity is not supplied to the transfer member,   the voltage of the second polarity in the second period and the third period is supplied to the transfer member,   the first period and the second period are periods during which a surface portion of surface portions of the image bearing member at a dark portion potential passes through the charging member,   the third period is a period during which the surface portion of the surface of the image bearing member at a bright portion potential passes through the charging member, and   the controller is further configured to determine the surface potential of the image bearing member based on a first charging current detected by the detection circuit in the first period, a second charging current detected by the detection circuit in the second period, and a third charging current detected by the detection circuit in the third period.   
     
     
         6 . The image forming apparatus according to  claim 5 , wherein
 the controller is further configured to determine the bright portion potential of the image bearing member by dividing a difference between the first charging current and the second charging current by a difference between the voltage of the first polarity supplied to the transfer member in the second period and the voltage of the first polarity supplied to the transfer member in the first period, to obtain a current change amount per unit voltage, dividing the third charging current by the current change amount to obtain a voltage, and subtracting the voltage from a dark portion potential of the image bearing member.   
     
     
         7 . The image forming apparatus according to  claim 6 , wherein
 the controller is further configured to determine the dark portion potential by dividing the second charging current by the current change amount.   
     
     
         8 . The image forming apparatus according to  claim 1 , wherein
 the controller is further configured to adjust the voltage of the second polarity used in the current detection period in accordance with a resistance value of the transfer member.   
     
     
         9 . The image forming apparatus according to  claim 1 , further comprising
 a sensor configured to detect an environmental condition of an environment in which the image forming apparatus is installed,   wherein the controller is further configured to adjust the voltage of the second polarity to be used during the current detection period according to the environmental condition.   
     
     
         10 . The image forming apparatus according to  claim 9 , further comprising
 a current detection circuit configured to detect a transfer current flowing through the transfer member,   wherein the controller is further configured to determine a target value of the transfer current based on the environmental condition, and change an output voltage of the second power supply until the transfer current detected by the current detection circuit reaches the target value, and the voltage of the second polarity is determined based on the output voltage of the second power obtained at a time when the transfer current reaches the target value.   
     
     
         11 . The image forming apparatus according to  claim 10 , further comprising
 a storage medium configured to hold a plurality of environmental conditions and a plurality of target values in association with each other in a one-to-one correspondence,   wherein the controller is further configured to obtain, from the storage medium, the target value corresponding to the environmental condition detected by the sensor.   
     
     
         12 . The image forming apparatus according to  claim 9 , wherein
 an adjustment period in which the voltage of the second polarity used in the current detection period is adjusted is located earlier than the current detection period.   
     
     
         13 . The image forming apparatus according to  claim 12 , wherein
 a waiting period for returning the surface potential of the image bearing member to 0V is provided between the adjustment period and the current detection period.   
     
     
         14 . The image forming apparatus according to  claim 1 , wherein
 the current detection period includes a first period and a second period,   an absolute value of the voltage of the first polarity in the first period is smaller than an absolute value of the voltage of the first polarity in the second period,   in the first period, the voltage of the second polarity is not supplied to the transfer member,   in the second period, the voltage of the second polarity is supplied to the transfer member, and   an adjustment period during which the voltage of the second polarity used in the second period is adjusted is provided between the first period and the second period.   
     
     
         15 . The image forming apparatus according to  claim 14 , wherein
 a waiting period for returning the surface potential of the image bearing member to 0V is provided between the adjustment period and the second period.   
     
     
         16 . The image forming apparatus according to  claim 1 , wherein
 the current detection period includes a first period and a second period,   an absolute value of the voltage of the first polarity in the first period is smaller than an absolute value of the voltage of the first polarity in the second period,   in the second period, the voltage of the second polarity is supplied to the transfer member, and   an adjustment period during which the voltage of the second polarity used in the second period is adjusted is provided within the first period or in parallel with the first period.   
     
     
         17 . The image forming apparatus according to  claim 16 , further comprising:
 a current detection circuit configured to detect a transfer current flowing through the transfer member; and   a sensor configured to detect environmental conditions,   wherein the controller is further configured to determine a target value of the transfer current based on the environmental condition, and   the controller is further configured to determine a voltage of the second polarity to be output in the second period based on the output voltage when the transfer current reaches the target value while changing an output voltage of the second power supply in the adjustment period.   
     
     
         18 . The image forming apparatus according to  claim 17 , wherein
 the controller is further configured to determine a voltage of the second polarity by adding a difference between the voltage of the first polarity applied to the transfer member in the adjustment period and the first period and the voltage of the first polarity applied to the transfer member in the second period to the output voltage when the transfer current reaches the target value.   
     
     
         19 . The image forming apparatus according to  claim 17 , wherein
 the light source is configured not to expose the image bearing member in the first period, and is configured to expose the image bearing member in the second period, and   the controller is further configured to control the second power supply to gradually increase the output voltage until the transfer current reaches the target value in the adjustment period.   
     
     
         20 . The image forming apparatus according to  claim 1 , wherein
 the first power supply is further configured to output a charging voltage that is the voltage of the first polarity to the charging member, and to output a transfer voltage that is the voltage of the first polarity to the transfer member and that changes in conjunction with the charging voltage.   
     
     
         21 . The image forming apparatus according to  claim 1 , wherein
 the polarity of the superimposed voltage is the first polarity.   
     
     
         22 . The image forming apparatus according to  claim 1 , wherein
 the voltage of the second polarity supplied to the transfer member from the second power supply is a transfer bias for promoting transfer of the toner image from image bearing member to the transfer material.   
     
     
         23 . The image forming apparatus according to  claim 1 , wherein
 the voltage of the first polarity supplied to the transfer member from the first power supply is a cleaning bias for re-transferring the toner adhered to the transfer member to image bearing member.   
     
     
         24 . An image forming apparatus comprising:
 an image bearing member;   a motor configured to rotationally drive the image bearing member;   a charging member configured to charge a surface of the image bearing member which is rotationally driven by the motor;   a light source configured to irradiate the surface of the image bearing member with light to form an electrostatic latent image;   a developing member configured to develop the electrostatic latent image using a toner charged to a first polarity to form a toner image;   a transfer member configured to transfer the toner image from the image bearing member to a transfer material;   a first power supply configured to generate a voltage of the first polarity and apply the voltage of the first polarity to both the charging member and the transfer member;   a second power supply configured to generate a voltage of a second polarity opposite to the first polarity and apply the voltage of the second polarity to the transfer member;   a detection circuit configured to detect a charging current flowing between the charging member and the image bearing member; and   a controller configured to control the first power supply and the second power supply to determine a surface potential of the image bearing member based on the charging current,   wherein the controller is further configured to control the first power supply to generate the voltage of the first polarity, to supply the voltage of the first polarity to the charging member as a charging bias, and to supply the voltage of the first polarity to the transfer member as a cleaning bias during an image forming period of forming the toner image,   the controller is further configured to control the second power supply to generate the voltage of the second polarity during the image forming period, and to supply the voltage of the second polarity to the transfer member as a transfer bias for promoting transfer of the toner image from the image bearing member to the transfer material,   the controller is further configured to, in a cleaning period for cleaning the transfer member, stop the second power supply while operating the first power supply, and   the controller is further configured to operate the first power supply and the second power supply in a current detection period in which the detection circuit detects the charging current, thereby applying a superimposed voltage generated by superimposing the voltage of the first polarity and the voltage of the second polarity to the transfer member, and to determine the surface potential of the image bearing member based on the charging current detected in the current detection period.